Exemplary embodiments relate generally to a semiconductor memory device and a method of reading out the same, and more particularly to a semiconductor memory device of reading out normal read data and over-sampling read data in a read operation and a method of reading out the same.
Semiconductor memory devices can be divided into a volatile memory device and a non-volatile memory device. The volatile memory device requires power to retain the stored information. On the other hands, the non-volatile memory device can retain the stored information even in absence of power supply.
With increasing demand for highly integrated memory devices, semiconductor memory devices in which multi-bit data are stored in a single memory cell are generally used. For example, in the non-volatile memory device in which multi-bit data is stored, threshold voltage distributions of adjacent memory cells may partially overlap with each other due to the narrow interval between each distribution.
FIG. 1 shows threshold voltage distributions of a known semiconductor memory device.
In the semiconductor memory device of FIG. 1, threshold voltage distributions of memory cells overlapping with each other are shown. In a read operation, data may be erroneously read out from memory cells having threshold voltages included in the overlapped parts. An error included in the read data may be corrected by using a memory controller in a read operation.